Your Amplifier is not set correctly. It is set too ‘cold’. Adjust the potentiometer to "warmer’,
That’s an other vacuum actuator, and if I remember correctly, it’s behind the box.
You will have to remove the dash pad to get access.
Slowly but steadily, you will get it right!
Best,
Aristides
Aristides,
Thank you again for all the helpful advice. I’m excited to check it out!
Danny
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All vents, except the defrost should be closed in ‘def’, Danny…
In ‘def’; no vacuum is applied to any vacuum actuator - and all vacuum devices goes to their default positions. In your case, the centre(!) vents wrongly have vacuum - and since there is no heat; the water valve also wro0ngly have vacuum. The side vents are manually operated and are always open, as Aristides mention - unless manually closed…
There is a special setting too for adjusting the linkages - I don’t know what procedure, or indeed ‘what’ the mechanic adjusted. The pushrods operated by the servo are adjustable - and the vacuum valve controlling the heater valve is cam operated…
That the system changes from heating to cooling while driving implies that the servo alters position - the reason for this is unclear. One possible test is, while the system is heating, is to disconnect the AC amp plug to see what happens while you drive on.
Or indeed to notice servo position when it is heating and when it is cooling - to clarify whether this behaviour involves the AC amp reacting to inputs, or some other system anomaly. And disconnecting the vacuum hose at the heater valve is an obvious test - including verifying that both heater core hoses are one hot and one warm. If not; there is no circulation through the core; which is either a closed valve ore a restricted core. Bear in mind that the AC compressor goes full bore at all times - and without reheating in the heater core all will be cold…
You probably have more than one fault - adjustments or otherwise. Have you consulted the mechanic about exactly what, and how, he adjusted…?
Frank
xj6 85 Sov Europe (UK/NZ)
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I was premature !!! Errands yesterday. I chose my Jeep. It and the Jaguar take turns. No heat wanted. AC felt really nice!!!
Carl
Frank,
Thank you for all this valuable information. I love this forum. I will share your email with my mechanic and we’ll work to resolve the issues. I agree, there is more than one thing going on.
I will report back once I get they system resolved.
Danny
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Or indeed any progress, Danny…?
Frank
xj6 85 Sov Europe (UK/NZ)
**
Frank,
My mechanic is coming today (he works from my house, which is so convenient) and I’m going to share your insights with him. I’m hopeful I’ll have some progress today. Fingers crossed!
Danny
Did you figure it out?
I just returned from vacation and drove the car for the first time today. The heat/air system is MUCH better. My mechanic adjusted the potentiometer warmer and the system seems to work properly. He may have adjusted it too warm and I need to drive the car more to see for certain. He also found another vacuum line that was crimped. Air still blows out the center face vents all the time, which must mean another vacuum issue, but it doesn’t really bother me.
As I’m writing this, I’ve been sitting for 3 hours waiting on a tow truck to pick up my car. The car started smoking a lot from between the radiator and the engine on the side of the compressor and smelling badly of something electrical burning. There was a loud rubbing noise as the belts were turning. It wasn’t running hot, there are no leaks, and there was no fire. I suspect my newly rebuilt air compressor seized. 
I finally got picked up after four hours. I hate seeing my beautiful car being towed.
I hope it’s my compressor, which is under warranty.**
Nothing anyone does with the system internally will cause the compressor to seize, Danny…
As you say, the rebuild might have been less than perfect - but if the belt was insufficiently tight, it would start slipping, and continue to do so with smell and smoke. However, did you turn the AC ‘off’ - and what happened then? Beside that, slipping belt will smoke - but the engine should still run…
Hate to see a Jaguar, particularly such a nice one, on a flatbed - but if this was a seized compressor; the compressor clutch won’t engage with the AC off, seized or not. A seized compressor clutch will keep the compressor engaged - and one solution then is to cut the belt, and drive on…
As an aside; the only adjustable potensiometer is on some versions of the AC amplifier. That adjustment is done by measuring cabin temperature - to verify that it is the same as the setting on the temp controller.
That the centre vents are open implies that the system is in cooling mode - and blowing hot may be caused by no refrigeration…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Cut belt, drive on. Been there done that. But, it was in my 85 F150 4x4 decades ago. I failed to pay attention to it’s impendimg failure. it cooled perfectly, but made a ton of noise…
Carl
I’m happy to report the compressor did fail. I’ve ordered a new one. The failed one, which was under warranty, was a rebuilt. Yes, it still made terrible noise even with the system turned off.
I didn’t think of cutting the belt. Kinda wished I had even though the tow was free.
The potentiometer was adjusted warmer and the system responded much better. It’s possible it’s a little too warm now and may need to be adjusted in the other direction a little. The center vents stay open all the time, even in cooling mode. I think there’s still a vacuum leak but frankly, it doesn’t bother me too much if they stay open all the time. So I may not go after that last vacuum leak, which I understand would require the top of the dash to be removed to find and fix. Geez, this system has required a lot of attention! Kind of like my gas tanks. :-/
Danny
**
You can test externally for a leak before eventually attending to it, Danny - only need a vacuum gauge…
Locate the vacuum reservoir, rear in the engine compartment - a flattened round tin with one vacuum hose. Connect gauge to the hose and run the engine - it should read manifold vacuum. Stop engine and watch the gauge - it should stay at manifold vacuum. If not there is a leak…
To locate a leak further; clamping of engine bay vacuum hoses is used. Follow the hose from the vacuum reservoir to a T- connection; one hose on the goes into the cabin through the firewall. One hose goes to a one-way valve, then down to the vacuum supply at the engine.
Again run the engine, reading manifold vacuum at the reservoir hose, then clamp the ‘cabin’ hose and stop the engine - vacuum should be retained. If leaking, the one-way valve has failed - no great matter.
Unclamp ‘cabin’ hose, run the engine and clamp the hose between the one-way hose and the ‘T’ - stop engine. If leaking; the leak is inside the cabin - indeed requiring inside access. To be addressed later at your pleasure…
Two points to make; one is that the centre vents are held open by vacuum - a vacuum leak cannot hold them open. Second; cabin temps are controlled by the temp selector, which is a potentiometer, between 65 and 85F.
However, while cabin is warming up, the system deliver max heating; there are no adjustments to increase this heating - it restricted by heater capacity and coolant temps. When the set temp is reached, the system mixes cool air from the outside and/or AC evaporator with hot air from the heater core to maintain cabin temp - in ‘auto’; fan speed drops to signal the system has gone into ‘blend’…
It’s ‘unfair’ to the system to relay on your feeling of heat or cold; a thermometer, placed near the cabin’s in-car sensor to evaluate system performance.
The point is that the temp control should adequately regulate cabin temp to your liking - and your lack of control indicates a problem that should not be solved by potensiometer adjustments. Without the compressor, the system should heat perfectly - only cooling is restricted in this situation; it has to rely on outside air temps…
Frank
xj6 85 Sov Europe (UK/NZ)
**
Wonder if the old glass tube with mercury thermometers still exist! I may have one around some where.
When I replaced the furnace thermometer with one that I could program I moved the ancint one to the shop. Mercury tube in it. It works, but must be dead nuts level…
Carl
Frank,
I really appreciate you consistently sharing your wealth of knowledge. Just in the last couple months you, and many others on this forum, have helped me enormously to get my car sorted out. Being a new Series III owner with a car that hadn’t been driven or tended to hardly at all the past 25 years, I’ve really needed the help. I can’t thank you and the other wonderful people on here enough.
I’ve printed your last post, as I’ve done with many of the others, and will share it with my mechanic.
I don’t know why the center face vents stay open all the time. Maybe the flaps are just stuck due to age. But the system does get hot when set near 85 and gets cold when set near 65. So the fact that the center vents stay open all the time doesn’t really bother me. I actually kind of like having heat coming out the bottom vents and the center face vents when in heating mode. It feels like it’s heating the car better than if heat were just coming out the bottom vents.
Cheers!
Danny
Danny:
I’m with you. Although my Jaguar’s AC is not yet charged !! I like the warm air from the center or defrost vents over the others.
My Jeep does have AC and Heat, I operate it’s slightly less complex system in a similar fashion…
And, me as well. Over the years I’ve printed a lot of J-L material. My collection of Jag lore is overwhelming!!!
Carl
Carl,
I’m glad I’m not the only one haha! Now if this car only had seat heaters… 
Danny
I hate seeing my car towed too. That’s why I bought a trailer. haha. Still not cool to see a Jag being drug around behind a vehicle. That is a really pretty car. I wish my Xj’s look that nice. I’ve got the same wheels on my green XJ6. I hate the spinners. They’re always in the way when it’s time to take the wheels off. hehe! I get a ton of complements though.
**
As you can learn from the post on my present predicament, Danny - do nothing rash…
A system that works imperfectly, but doing its job, is better than a system not working at all due to owner fiddling!..
Frank
xj6 85 Sov Europe (UK/NZ)
**
Thanks, Mark. I really love the car but it’s been taking a toll on my patience for sure. It’s been one thing after another since I bought it. But I think I see light at the end of the tunnel. Fingers crossed!
Regarding the wheels, I love them but they’ve been a bit of a challenge too. One of them has a slow leak. It’s not the tire. I can’t find anyone who services wire wheels. I could send it to Dayton but what a pain. An option is to have a tire shop put a tube but finding a shop that does that is proving to be a challenge too. If anyone happens to know anyone in the Seattle area who services wire wheels or will put a tube in a tire, I’d love to have the recommendation.
